1. Field of the Invention
The present invention relates to polymeric fibrids that contain particulate matter. More specifically, the invention concerns such fibrids which are particularly suited for use as obscurants of radar, electromagnetic waves and the like.
2. Description of the Prior Art
Effective means have long been sought for hiding the movement of troops and equipment from visual detection or from detection by means of devices that depend on reflection or absorption of electomagnetic waves, such as radar or infra-red waves. Smoke screens, tinsel foil dropped from airplanes and the like have been used in the past. However, more effective obscurant means are needed.
Though not related to the above-described problem, fibrids formed from organic polymers and processes for their production are known, as for example, from Morgan, U.S. Pat. No. 2,999,788. Morgan also discloses that various materials can be added to the fibrids, such as dyes, antistatic agents, surfactants, fillers such as silica, titanium dioxide or sand, pigments, antioxidants, electroluminescent phosphors, bronze powder, metal filings, and the like. Parrish et al, U.S. Pat. No. 2,988,782, discloses a specific shear-precipitation process for making fibrids, and certain equipment (tube fibridators) that is particularly suited for carrying out the process. Parrish et al also discloses the inclusion of fillers and pigments. Gross, U.S. Pat. No. 3,756,908, discloses a process for preparing fibrids of aramid polymers. Miyanoki, U.S. Pat. No. 4,146,510, discloses various flash-spun polymeric fibrids which a variety of finely divided that can pass through a less-than-100-mesh screen and are no more than 500 microns in nominal size, for use in forming pulps, sheets, etc. Rosser et al, U.S. Pat. No. 4,397,907, discloses a supercooled fiber-forming polymer solution which is combined with metal, graphite, lead oxide, iron oxide or other particles and then the polymer is formed into 500 to 10.sup.7 Angstrom particles. The particles are trapped by or entangled with, but not encapsulated by, the polymeric particles, which then are optionally further beaten.
Some of the above-described particles have found use in papers and other nonwoven products, but none are disclosed as being air-dispersible.
Hugdin et al, U.S. Pat. No. 4,582,872 discloses that metallized polymers which are produced by melting metal and polymer together are suited for shielding electromagnetic interference. Luksch, U.S. Pat. No. 3,505,038, discloses "hair-like metal fibrils" that are dispersible or conveyable in air.
A purpose of the present invention is to provide loaded fibrids that can remain air-borne for a sufficiently long time (i.e., have a sufficiently slow settling rate) to be effective as electromagnetic-wave obscurants for hiding military operations.